The present invention was developed to fill a need for a device which efficiently converts thermal energy to electrical energy with power densities large enough for practical applications.
Current pyroelectric power converters include stacked capacitors having temperature dependent capacitance and the use of reeds which serve as thermal switches and are caused to vibrate by the flow of vapor carrying heat between stages, thereby pulsing the heat at the proper frequency and phase through the stacked capacitors. Another known device exploits a somewhat different concept in an energy conversion system in which a first material within the region between the electrodes of a capacitor is replaced, following charging of the capacitor, by a second material having a lower dielectric constant than the first material. The capacitor is then discharged and the first material is restored to the region between the capacitor electrodes for subsequent recharging.
Another approach uses a material with a dielectric constant different from that of a vacuum which is inserted between capacitor electrodes. In this case, mechanical work is performed against an electric field and the device is essentially the same as an electromagnetic motor. This approach is different from using pyroelectric materials and electrocaloric effect, because it uses capacitance change at a constant charge. In the case of pyroelectric action, the charge is changing according to the temperature change. If the relative dielectric constant is also changing with temperature, it is a side effect.
A further approach uses electrocaloric effect for pyroelectric conversion of heat into electricity. However, this approach has a large time constant because the pyroelectric material is mechanically moved from the hot to cold zone. With respect to devices deriving electrical energy by thermally cycling capacitors with temperature dependent properties, the small efficiencies and low power densities have apparently precluded their use in any practical application for the production of electrical energy.
There remains a need to provide a more satisfactory solution to converting thermal energy to electrical energy.